As known in the art, electronic control units (ECUs) that are installed in a vehicle are often network-connected to configure a vehicle network system that allows the ECUs to transfer information with one another. Controller Area Network (CAN) is a communication system that configures such a vehicle network system.
CAN is provided with a function for detecting communication errors. More specifically, in CAN, an ECU that transmits data on the CAN bus monitors signals on the CAN bus when transmitting data and compares the monitored signals with signals based on the transmitted data. When the compared signals are in correspondence with each other, the ECU determines that communication has been correctly performed. When the compared signals are not in correspondence with each other, the ECU determines that a communication error has occurred.
In accordance with the CAN specification, normal communication is performed when the count number of communication errors cumulated by the ECU that transmits data is less than 256, and communication of the ECU is stopped when the count number reaches 256. When communication of the ECU is stopped in this manner, communication is restarted when the communication error count is reset. Patent document 1 describes one example of a technique for automatically resetting the communication error count to restart communication.
Patent document 1 describes a communication recovery determination method that clears the communication error count number after CAN communication is stopped and performs communication (transmission) only once after a predetermined time (e.g., 100 ms) elapses. In the process that performs communication (transmission) only once after the predetermined time elapses, when a communication error is detected, a process for performing communication (transmission) only once after a predetermined time elapses is repeated. When a communication error is not detected, normal communication is restarted.
Patent Document 1: Japanese Laid-Open Patent Publication No. 2001-339412